Re: [PATCH] busybox: avoid circular dependency when using initramfs

[Stefan Agner <stefan@agner.ch>]

On 2016-09-06 09:35, Khem Raj wrote:
>> On Sep 4, 2016, at 1:25 PM, Stefan Agner <stefan@agner.ch> wrote:
>>
>> The kernel does not automatically mount devtmpfs when using initramfs
>> based booting (even when using CONFIG_DEVTMPFS_MOUNT). If the rootfs
>> is built with USE_DEVFS=1 (which is the default), the system ends up
>> with a completely empty /dev to begin with.
>>
>> Busybox uses the first entry in inittab slightly different than
>> other init systems:
>> <id>: WARNING: This field has a non-traditional meaning for BusyBox init!
>>
>> The id field is used by BusyBox init to specify the controlling tty for
>> the specified process to run on.  The contents of this field are
>> appended to "/dev/" and used as-is.
>>
>> Since /dev/null is not there yet, Busybox throws errors instead of
>> executing the commands, and hence never mounts devtmpfs:
>> init started: BusyBox v1.24.1 (2016-09-04 11:53:14 PDT)
>> can't open /dev/null: No such file or directory
>> can't open /dev/null: No such file or directory
>> can't open /dev/null: No such file or directory
>> can't open /dev/null: No such file or directory
>> can't open /dev/null: No such file or directory
>> can't open /dev/null: No such file or directory
>> can't open /dev/null: No such file or directory
>>
>> Avoid this circular dependency by not specifing <id>. With that
>> Busybox ends up using the stdio of the init process and executes
>> the inittab just fine.
> 
> This looks good. Have you also tested it when using busybox/mdev as main
> init system just not in initramfs
> 

I remember that I tried it once with squashfs and ramdisk, which, as far
as I can recall, behaves as if it is a regular rootfs wrt devtmpfs
mount...

--
Stefan